This application claims priority on Japanese Patent Application No. 11-143952 filed on May 24, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to structures for housing motors. More particularly, the present invention relates to a structure for housing in an electric power tool a motor, such as a DC motor or AC motor, that includes a stator, a rotator, and brushes.
2. Description of the Related Art
Various structures for accommodating a motor in an electric power tool have been proposed in recent years. For example, Japan Published Unexamined Patent Application No. 10-29173 discloses one such structure which includes a bearing for supporting the stator, a support element for supporting the bearing for the rotator, and another support element for supporting the brushes. Additionally, in order to prevent faulty commutation or a break in the wire due to vibration caused by rotation of the motor, this structure further includes elastic bodies, such as O-rings, on the bearing for the stator and the support element for the bearing.
Another structure for accommodating a motor in an electric power tool is disclosed in Japan Published Unexamined Utility Model Application No. 7-30572, in which a motor includes a rotator and a stator accommodated within the motor""s casing. Furthermore, to prevent excessive vibration of the motor and its associated problems, elastic material, such as pieces of rubber, is interposed between the support element for the brushes and the lid of the casing.
While the foregoing structures partially achieve their intended objectives, they are not free from certain problems and inconveniences. For example, as each of the examples attempts to solve the problem of vibration by separately providing an elastic body for different motor elements, such as the support element for the bearing for the rotator and the support element for the brushes, the effect has proven limited. Particularly, the brushes and the rotator tend to vibrate in different phases, which may cause wobbling of the rotator with respect to the brushes. In turn, this often causes faulty commutation of the motor or even shortens the service life of the brushes.
In view of the above-identified problems, an important object of the present invention is to provide an improved structure for accommodating a motor in an electric power tool which minimizes vibration of the motor during operation.
Another object of the present invention is to provide an improved structure for accommodating a motor in an electric power tool which effectively prevents adverse effects on the commutation of the motor and prolongs the service life of the brushes.
The above objects and other related objects are realized by the invention, which provides an improved structure for accommodating a motor having a stator and a rotator. The structure comprises: a housing; a stator support for supporting the stator of the motor; a rotator bearing for supporting the rotator of the motor; a bearing support for supporting the rotator bearing; a brush holder for holding brushes for the motor, the brush holder being integrally formed with the bearing support, and elastic means interposed between the brush holder and the housing, the elastic means separating the brush holder and the bearing support from the housing while elastically supporting the brush holder and the bearing support within the housing.
In this structure, the brush holder and the bearing support are integrally formed and separated from the housing, whereas the elastic means between the brush holders and the housing elastically supports the integrated two elements. Therefore, the structure effectively reduces harmful vibration and prevents breakage in the wiring during the operation of the motor. This structure further allows the brush holder and the bearing support to vibrate substantially in the same phase, thus preventing wobbling motion of the bearing support with respect to the brush holder. Hence, proper commutation of the motor is ensured and the service life of the brushes are prolonged. Moreover, as the brush holder incorporates the bearing support, the rotator can be assembled with the bearing with a high degree of precision. Additionally, the integration of the bearing and the bearing support eliminates the need for providing separate elastic bodies, thus isolating vibration with a fewer number of elements.
According to one aspect of the present invention, the elastic means includes a plurality of cylindrical rubber pins.
According to another aspect of the present invention, each of the rubber pins has a first end and a second end, with the first end being fitted in an outer surface of the brush holder and the second end being fitted in an inner surface of the housing, thereby spatially separating the brush holder and the bearing support from the housing and concomitantly providing elastic support to the brush holder and the bearing support within the housing.
According to still another aspect of the present invention, the brushes have a common longitudinal axis and four mutually parallel rubber pins are oriented parallel to the longitudinal axis the brushes.
According to yet another aspect of the present invention, the housing has a longitudinal axis along which the stator of the motor is coaxially disposed, whereas the brush holder and the bearing support are generally circularly shaped and coaxially disposed about the axis of the housing.
According to one feature of the present invention, the structure further comprises at least one bridge for connecting the bearing support to the brush holder.
According to another feature of the present invention, the elastic means are adapted to allow the brush holder and the bearing support to vibrate in substantially the same phase during the operation of the motor.
According to still another feature of the present invention, the plurality of brushes are a pair of brushes removably mounted in the brush holders and the structure further includes a pair of brush caps removably attached to the brush holders for covering the brushes such that, when the brush caps are removed, the brushes are exposed for replacement.
Other general and more specific objects of the invention will in part be obvious and will in part be evident from the drawings and descriptions which follow.